Upstream doesn't have this issue. Seems we do some auto optimization to the
"read ahead" value:
# blockdev --setra 678 /dev/loop0
# blockdev --getra /dev/loop0
672
# lvcreate -n testlv -L4m testvg /dev/loop0
# blockdev --getra /dev/testvg/testlv
1024
# blockdev --setra 4096 /dev/loop0
# blockdev --getra /dev/loop0
4096
# lvcreate -n testlv -L4m testvg /dev/loop0
Logical volume "testlv" created.
# blockdev --getra /dev/testvg/testlv
4096